The present invention discloses a novel adjustable angle tool joint of two pipe sections that form part of a drill string casing, for example, a deep drilling tool casing for a directional drilling motor.
A known pipe joint of this type, as disclosed in U.S. Pat. No. 4,813,497, serves to impart a neutral axial alignment to the pipe sections that are to be joined and this alignment can be varied within a given bending angle range. This pipe joint consists of a total of five components and includes a tubular inside part that can be screwed in at one end and which also has an outside thread coinciding with the inside thread of one of the pipe sections to which it is to be joined. The outside thread of this inside part has a thread axis which forms an angle with the main axis of the inside part equal to half the size of the maximum possible bending angle for the pipe joint.
A tubular connecting part is provided on the inside part so that the connecting part can move axially over and rotate about the main axis of the inside part. This tubular connecting part has an outside thread on one end that can be screwed with the inside thread of the other pipe section to be joined. This outside thread has a thread axis which also forms an acute angle with the main axis of the inside part and which corresponds to half the size of the maximum possible bend angle of the pipe joint. The connecting part also has facing teeth on the end facing away from its outside threads, and by means of these teeth it engages with the facing teeth on a tubular outside part which can move axially over the inside part but which is prevented from turning about the main axis of the inside part.
The outside part and the connecting part are held in mutual engagement by two nuts, each of which sits with its outside thread on the inside part in a screwed engagement, and the parts are held in compressive engagement on their facing ends with the other ends of the outside part and the connecting part facing away from each other. By releasing the compressive engagement between the outside part and the nut engaged with it, the outside part can be moved with the connecting part and the connecting part can be turned to the desired extent relative to and about the main axis of the inside part. The locking engagement between the outside part and the connecting part can be restored and secured by tightening the nut acting on the outside part.
Depending on the alignment of the connecting part relative to the inside part, a bend angle can be adjusted between the axes of the pipe sections to be connected with this pipe joint. This bend angle has a range whose minimum value is zero and whose maximum value is based on the sum of the angles about which the hinge axes of the connecting thread for the pipe sections to be joined are bent from the main axis of the inside part of the pipe joint.
Such a pipe joint is complicated in its design and handling, has a reduced strength in comparison with the strength of the joined pipe sections, permits angle changes only in the stages determined by the facing teeth between the outside part and the connecting part, and does not present a closed exterior contour in the area of the joint.
In another known pipe joint design including an adjustable angle of bend between the pipe sections to be joined, as disclosed in U.S. Pat. No. 4,817,740, two pipe bodies which are part of the pipe joint are connected directly to each other by way of threads whose axes are bent at an angle. The bend angle between the pipe sections of the drill casing to be joined changes with the length of engagement of the angled threads of the two bodies that are to be screwed together. The engagement length is determined by spacers placed between the two pipe bodies.
Such a design is also complicated structurally and in its field handling, permits only stepwise adjustments in the bend angle between the pipe sections to be joined as a function of the gradation in the available spacers, and causes an adjustment in the axial distance between the pipe sections to be joined when the angle of the bend is adjusted.
There is also a known pipe joint where the pipe sections of a drill casing are joined together with a screw connection, as disclosed in U.S. Pat. No. 4,553,614, whereby a spacer is provided and can be inserted between the facing ends of the pipe sections to be joined. The spacer consists of segments that can be joined to form a ring between the end faces of the pipe sections to be joined. Such a pipe joint makes it possible to adjust the mutual spacing of the pipe sections to be joined without detaching the mutual screw connection of the pipe sections. Such a spacing adjustment makes it possible, for example, to vary the pre-tension of an axial spring arranged between the shoulders of the pipe sections that are to be connected, but it is also associated with changes in the rotatory alignment of the pipe sections to be joined.